1. Field of the Invention
The present invention relates to a process for preparing fluorinated diol compounds by hydrogenating fluorinated precursor compounds.
2. Description of Related Art
There has been significant interest recently in the synthesis of fluorine containing diol molecules. These fluorinated diols have been used as precursors in the synthesis of monomers for the next generation of photoresist materials, for example, as described in U.S. Pat. Nos. 7,067,691, 7,495,135, and 7,442,828.
The fluorinated diols can be made by the reaction of hexafluoroacetone with various carbonyl compounds followed by the reduction of the carbonyl group to make the desired fluorinated diols. The fluorinated diols can be converted into their acrylate/methacrylate esters for use as monomers.
U.S. Pat. No. 3,662,071 teaches a process for the synthesis of various fluorinated diols (Scheme I) by (1) reacting hexafluoroacetone (or chlorodifluoro acetone) with a suitable ketone at 160° C. and (2) reducing the keto-alcohol made in step 1 with aluminum isopropoxide and isopropanol. This reduction method has the drawback of generating significant aluminum waste that has to be disposed of. This leads to a lower yield because some of the organic product is left behind in aqueous phase and there is an increased cost associated with getting rid of the aluminum waste.

U.S. Pat. No. 7,205,443 solves this problem (Scheme II) by reducing the keto alcohol made by reaction of hexafluoroacetone and carbonyl compound, with hydrogen, over ruthenium catalyst.

This patent further teaches that this reduction can only be effected using ruthenium as catalyst. The patentees mention that the use of palladium and platinum gave poor results. An example from the experimental section shows less than 5% conversion with platinum as the catalyst and essentially no conversion using Pd as the hydrogenation catalyst (Scheme II).
U.S. Pat. No. 3,440,285 claims a process of reacting aliphatic aldehydes with fluorinated ketones such as hexafluoroacetone to generate fluorinated hydroxy substituted aldehydes. These hydroxy aldehydes were then reduced to fluorinated diols using known reagents like lithium aluminum hydride, sodium borohydride, lithium borohydride or aluminum isopropoxide (Scheme III). These reduction methods are either not easily scalable or generate significant metal waste by-products. This patent also teaches that the reduction of the hydroxy aldehyde can be achieved by hydrogenation over rhodium, platinum or using Raney nickel catalyst. No mention is made of using the much cheaper palladium as a catalyst to affect this transformation.

What is needed is a cleaner process that does not generate waste and that is preferably continuous and uses less expensive catalyst.